Field of the Invention
The present invention relates to a switching regulator incorporating a transistor which ensures stable operation and high operating efficiency and further enables making in compact size with higher frequency.
The switching regulator of this type generally comprises, in principle, a switching transistor (1), a smoothing reactor (2), a smoothing condenser (3), a commutation diode (4) and a control circuit (5) as shown in FIG. 1 and FIG. 2. Moreover, (10) and (11) are a d-c power terminal and (42) and (43) are an output terminal.
FIG. 1 shows a series type constructed by connecting said transistor (1) in series with a load (a so-called voltage dropping chopper type) and FIG. 2 shows a parallel type constructed by connecting the transistor (1) in parallel with the load (a so-called voltage increasing booster type). A practical circuit constructed based on the principle of FIG. 1 is shown in FIG. 3. In FIG. 3, in order to increase the current amplification factor of the main transistor (1), said main transistor (1) and an auxiliary transistor (6) are connected like a Darlington circuit or complementary circuit and further a control transistor (7) is connected between the main transistor and a negative power terminal (11) to assure allowance with respect to voltage across positive and negative power terminals (10) and (11).
Also in a circuit constructed for the purpose of obtaining large output, as shown in FIG. 4, a transformer (8) is connected between the base and emitter of the main transistor (1) thereby to raise the whole availability of the main transistor (1) by increasing the current amplification factor of the main transistor (1) and also disconnecting electric potential as desired according to the winding ratio of said transformer (8).
Even though the means shown in FIG. 4 is taken, however, there are the following shortcomings. The present invention has obviated these defects completely. First, the defects involved in the circuit of FIG. 4 are analysed. (a), (b), (c) and (d) in FIG. 5 are the collector voltage (V.sub.c), collector current (I.sub.c), base current (I.sub.b) and voltage (V.sub.eb) across emitter and base of the main transistor (1) in FIG. 4, respectively.
And, (T.sub.on) and (T.sub.off) denote ON time and OFF time of the main transistor (1), (T.sub.o) is a time that base current of the main transistor (1) is supplied by energizing a control transistor (7) and (T.sub.s) is the storage time of the main transistor (1) after said control transistor (7) is deenergized.
The circuit in FIG. 4 is so constructed as to control output voltage by controlling said (T.sub.on) and (T.sub.off) with a control circuit (5) and when giving an account of (d) in FIG. 5 then, it is seen that voltage (V.sub.eb) across the emitter and base of the main transistor (1) is, on the other hand, the secondary voltage of the aforesaid transformer (8). The voltage time products, i.e., positive and negative hatched parts (A) and (B) in FIG. 5 must be equivalent accurately. For instance, provided that the values of the voltage across emitter and base in positive application and negative application are equal, T.sub.on should become almost equal to T.sub.off1. Therefore, when a suitable means is taken for the base circuit, the time can be reduced to T.sub.off2 as given by the characteristic shown by short dashes in FIG. 5; however for T.sub.on, T.sub.off2 is a controllable limit.
In this case, too, the time products (A) and (C) are equivalent as seen from FIG. 5.
In any way, using the transformer (8) in asymmetrical form positively and negatively causes various obstacles. To be concrete, in time T.sub.r after time T.sub.off1, voltage (V.sub.eb) across emitter and base should become zero as the transformer (8) is saturated in negative direction. However actually, as shown by short dashes in FIG. 5, voltage (V.sub.eb) across emitter and base fluctuates, whereby the collector current (I.sub.c) of the main transistor (1) is induced as shown by the characterictic (D) in FIG. 5 (b), resulting in the main transistor (1) working unstably.
Thus, the description about the series type has been given above and it is the same as with a case where the transformer is provided in the parallel circuit shown in FIG. 2.